Bows have been used for archery and hunting for hundreds of years and are available in a variety forms, including long bows, recurve bows, crossbows, compound bows, and several other types. All bows are generally configured to propel an arrow. Due to current innovations, the compound bow is the most commonly used type of bow. However, the recurve bow is also widely known and used. In typical recurve bows and long bows, as a bowstring is drawn, the limbs of the bow are bent inward. The bending of the limbs stores a significant amount of energy in the bow structure known as draw weight, often measured in pounds of force required to maintain the limbs of the bow in a given bent position. Upon release of the bowstring, the bent limbs rapidly return to their original shape. As the bent limbs rapidly return to their original shape, a significant amount of kinetic energy is translated to the bowstring, thrusting it forward, which in turn propels an arrow.
Compound bows differ from recurve bows in that wheels, cams, and/or eccentrics are attached to the free ends of the limbs. These eccentrics provide a mechanical advantage in bending the limbs of the bow. Additionally, compound bows provide what is known as “let-off”. “Let-off” is a point in a draw at which only a fraction of the originally applied force is required to maintain the limbs of the bow in a position that maximizes energy storage. Let-off is often measured as a percentage of force that is no longer required to maintain the limbs in the maximally bent position. Thus, it might be said that a given compound bow has an 80% let-off, meaning that the force required to maintain the bow at a drawn position is reduced by 80% compared to the draw weight.
Many of the latest innovations regarding bows are directed toward reducing undesirable vibrations, recoil, and noise during use. During operation, an arrow is nocked (secured to the bowstring) and the bowstring is drawn to full draw. This causes the limbs to bend and store energy that is subsequently released to propel an arrow. When the bowstring is released, most of the kinetic energy stored within the limbs is transferred to the bowstring, which propels the arrow. Ideally, all the energy would be transferred to the arrow. However, in reality only between 70-85% of the stored energy in traditional compound bows is transferred to the arrow. The remaining portion of the energy is transferred back into the bow and to the user. This returned energy is called recoil. Recoil is typically manifest as unwanted vibrations that reduce a user's accuracy.
In addition to recoil, the release of the bowstring, eccentrics, and limbs produces sound. The sound produced is often sufficiently loud to alert wild animals of the presence of the archer, causing them to jump or move. That is, the noise causes the animal to “jump the string”, resulting in a miss or a non-fatal strike. Consequently, bows configured for quieter operation are desirable over traditional compound bows.
Numerous recent improvements to compound bows are centered on improving the recoil, noise, and let-off. It is desirable to have a sufficient let-off while minimizing the noise and recoil. The use of eccentrics, while providing sufficient let-off, creates additional noise. Additionally, both recurve and compound bows rely on the bending of the limbs to store and rapidly return energy. This results in significant recoil as the limbs lurch forward upon release. Recent improvements are only marginally effective and often result in a reduction in arrow speed. For example, stabilizers and vibration-reduced limbs absorb energy that ideally would be transferred to the arrow.
Furthermore, as previously stated, compound and recurve bows rely on the bending of the limbs and rotation of eccentrics of the bow to store energy. In addition to wasted energy being expended as noise and vibration, as much as 45% of the stored energy is expended in returning the limbs to their original state. The amount of energy expended in restoring the limbs to the undrawn position is largely dependent upon the weight of the limbs and the distance they are displaced at full draw. Consequently, various methods have been contrived to reduce the weight and/or amount of limb deformation. However, in order to increase the draw weight, limbs are typically made wider and/or thicker. The formation of wider and/or thicker limbs, absent a material change, typically increases the weight of the limbs, thereby decreasing the efficiency. Accordingly, there is a long felt need for bows having increased efficiency, reduced noise and recoil, adequate let-off, and sufficient draw weight.